Urinary Tract Infection (UTI): Given the combination of nausea, vomiting, diarrhea, and hematuria, a UTI is a plausible diagnosis, especially if the patient is sexually active or has a history of UTIs. The presence of blood in the urine (hematuria) is a common symptom of UTIs.

Gastroenteritis: This condition, often caused by viral or bacterial infections, can lead to nausea, vomiting, and diarrhea. If the patient has a severe case, it might also lead to dehydration, which could potentially cause kidney issues leading to hematuria.
Kidney Stones: While more common in older adults, kidney stones can occur in younger individuals and cause severe pain, nausea, vomiting, and hematuria. The pain can sometimes radiate and cause gastrointestinal symptoms.
Pregnancy-related Conditions: Given the patient's age and symptoms, pregnancy-related conditions such as a miscarriage or an ectopic pregnancy should be considered, especially if the patient is sexually active and not using contraception. These conditions can cause bleeding and abdominal pain.

Septic Shock: Although less likely, septic shock from a severe infection (e.g., pyelonephritis, severe gastroenteritis) is a life-threatening condition that must be considered. Symptoms can include nausea, vomiting, diarrhea, and in severe cases, hematuria due to disseminated intravascular coagulation (DIC).
Ectopic Pregnancy with Rupture: This is a medical emergency that can present with abdominal pain, vaginal bleeding, and potentially hematuria if there's internal bleeding affecting the urinary system.
Toxic Shock Syndrome: Caused by bacterial toxins, this condition can arise from infections and lead to severe symptoms including nausea, vomiting, diarrhea, and potentially hematuria due to multi-organ failure.

Hemolytic Uremic Syndrome (HUS): A rare condition that can cause hematuria, HUS is often associated with diarrhea caused by E. coli O157:H7. It leads to kidney failure and can present with nausea and vomiting.
Thrombotic Thrombocytopenic Purpura (TTP): A rare blood disorder characterized by the formation of blood clots in small blood vessels throughout the body, which can lead to a variety of symptoms including hematuria, nausea, and vomiting due to multi-organ dysfunction.
Vasculitis: Certain types of vasculitis, such as IgA vasculitis (Henoch-Schönlein purpura), can cause hematuria, abdominal pain, and gastrointestinal symptoms, although they are less common in this age group and presentation.